More than 400 patients have had phonocardiography using a high frequency microphone and accelerometer system. The input is digitized and fast transform fourier analysis applied to the wave fora. Energy in dB versus frequency plots are obtained as are impact or closure sounds to determine synchrony of occluder or leaflet closure. Signatures of normal opening and closing sounds have been obtained. The data were obtained from porcine valves (71 aortic, 124 mitral) and mechanical valves (138 aortic, 58 mitral). More than 100 patients have had the sounds of their prosthetic device measure more than once. Analysis have shown for the aortic porcine that the peak frequency of the systolic ejection murmur is tightly correlated to the frequency of maximal closure energy more than 20 valves have been shown to be dysfunctional both by energy spectra analysis and cardiac catheterization studies. Replacement of the fatigued prosthetic valve has been performed in most cases. Pathologic studies confirm marked leaflet calcification and fatigue. Several more years of tracking the same patient will be required before the predictive value of acoustic energy spectra recording can be established as a screening method for patients with bioprosthetic valves.